Radiation emitting devices such as semiconductor lasers typically comprise a body of semiconductor material having opposed end faces in which an active layer is positioned between two cladding regions of opposite conductivity. One of the end faces typically has a reflective coating thereon and the other end face is partially reflective such that radiation produced in the active layer is partially reflected into the semiconductor body by an end face toward the opposing end face, thus forming a resonant cavity. When the current is sufficiently increased above some threshold value, the increase in gain causes lasing action to occur. Lasers emit a narrow band of highly coherent radiation and this coherent radiation may be undesirable in some applications, such as fiber optic gyroscopes.
Superluminescent diodes (SLDs) provide a high power output of broad band low coherent radiation. An SLD typically has a structure similar to that of a laser, with lasing being prevented by antireflection coatings being formed on the end faces. Reflective coatings are typically avoided in these devices since radiation generated within the device will likely be reflected between the end faces resulting in high spectral modulation or lasing action. Spectral modulation is the percentage ratio of the difference between the maximum and minimum power output divided by the sum of the maximum and minimum power output and low spectral modulation is 5% or less modulation. It would be desirable to have an alternative optical system in which the output power of these low coherence light-emitting devices is increased.